Styrenic copolymers such as styrene-acrylonitrile-based copolymers (SANs) can have excellent elasticity and heat resistance, and thus have been used in various industries requiring heat resistance. For example, heat resistance styrene-acrylonitrile-based copolymers (SANs) have been used for electrical and electronic parts, interior/exterior materials for automobiles, heat-resistant plastic containers, etc.
Heat resistant styrene-acrylonitrile-based copolymers (SANs) have been used in the form of an α-methylstyrene-styrene-acrylonitrile resin obtained by terpolymerizing α-methylstyrene, styrene, and acrylonitrile. Also, other monomers are often added, and prepared into multiblock copolymers so as to realize a higher level of heat resistance.
However, since α-methylstyrene has a low ceiling temperature, it has a slow reaction speed upon copolymerization, and can require a high temperature condition and a long reaction time. In this case, the economic feasibility and efficiency upon preparation of copolymers may be degraded.
Meanwhile, in preparing the styrene-acrylonitrile-based multiblock copolymers, it can be very difficult to adjust a polymerization speed and heat generated in the reaction. When the polymerization speed upon the preparation of the copolymers is very slow, productivity is lowered. When the polymerization speed upon the preparation of the copolymers is too fast, however, conversion rate of the copolymers can be reduced. Also, when the heat of the reaction and a process temperature upon polymerization are high, discoloration resistance may be reduced due to an increase in a thermal history applied to the copolymers.
Therefore, when other monomers are added to prepare a copolymer, conventional polymerization methods use solution polymerization or emulsion polymerization. However, the solution polymerization has a problem in that it requires a solvent recovery system and a separate solvent bath, resulting in a decrease in productivity and an increase in manufacturing cost. When the emulsion polymerization is used, it has a disadvantage in that processes are complicated, the productivity is poor, and it does not work easily.
Accordingly, there is a need for methods for preparing an aromatic vinyl based copolymer, which can reduce the thermal history applied to the copolymers during a preparation process, and simultaneously improve productivity and economic feasibility due to a short reaction time and a high conversion rate of the copolymer.